Hi,
Until a few month ago, Youtube had their partner-program which puts ads in your videos and pays you for it.
Now they let anybody join it , and they call it “Monetize your videos”
Basically once you join the program you “monetize” each of your original-material clips (they have to be 100% yours including audio). Then you choose the ad-type for each clip and you get paid once users click on it.

If you get a lot of viewers it’s a good program for you! no spam
Hope this helps, Elad.

I have been a Youtube Partner for a while, and have made very little money, like not even three digits. In my opinion it’s not worth it to have an ad at the front of your video unless you’re consistently getting a lot of views.

But if you want a little (and I mean a little) extra cash then go for it!